Apparatus for drilling well boreholes



y 27, 1954- I '1". v. MOORE- 2,634,835

. APPARATUS FOR DRILLING WELL BOREHOLES Filed July 26, 1950 I -iCYLIMD-QICAL.

- ELEMENT Q T Azme.

' Z PISTON HEAD 4 Poms FIQ-Q a 5 :DQIVE. BQSHIMG A Q, TOOL QJonuT E oxNo'z'z-ha HyQQ Thomas V. Mo orc Unvemaor abtaorneq Patented July 27,1954 APPARATUS FOR DRILLING WELL BOREHOLES Thomas V. Moore, Manhasset,N. Y., assignor to Standard Oil Develo ration of Delaware pment Company,a corpo- Application July 26, 1950, Serial No. 175,932

1 Claim. 1

The present invention is concerned with an improved apparatus fordrilling well bore holes. The invention is particularly concerned with anovel bottom hole assembly by which it is possible to employ an improvedmethod of exerting the necessary force on the bit during the drillingoperation. In accordance with the present in vention the required forceon the bit during a drilling operation is secured by utilization of thehead of the drilling fluid within the drill stem. The art of drillingwell bore holes into subterranean areas of the earth has beenextensively developed. A wide variety of drilling bits, associatedapparatus and various techniques have been utilized. However,conventional techniques for rotary drilling apply the required force tothe bit by allowing the weight of the drill string to partially rest onthe bit. This process while entirely satisfactory has a number ofinherent difiiculties. For example, part of the drill pipe may be incompression resulting in buckling of the pipe which in instances causesthe hole to deviate from the vertical. Furthermore, the stress induceddue to the buckling and unbuckling oi the compressed pipe results incorrosion fatigue. To reduce this difiiculty, drill collars, which areheavy lengths of pipe, are used. These are expensive, and are subject tofrequent failures. Another disadvantage is that the friction against thewalls of the hole causes the drill pipe to Wind up with the result thata substantial amount of bouncing of the bit occurs on the bottom of thehole. This aggravates the wearing of the cutter hearings in rock bits.It has now been discovered that these disadvantages are overcomeproviding the force on the bit is secured by a method other than byallowing the weight of the drill string to partially rest on the bit.The improved method of the present inven tion is secured by utilizing anovel bit assembly wherein the force on the bit is secured by theutilization of the head of the drilling fluid in the drill stem.

The present invention may be readily understood by reference to thedrawing illustrating one embodiment of the same. Figure 1 of the drawingillustrates the apparatus of the present invention attached to the lowerend of a drill string disposed in the earths substrata in a well bore.Figure 2 is a cross-sectional view taken along the line II-II ofFigure 1. Referring specifically to the drawing the lower end of a drillstring I is shown positioned within well bore hole 8. The bit assemblyof the present invention is shown attached to the end of drill string l0. The assembly comprises a cylindrical element l which containspositioned therein a piston assembly. The piston consists of a pistonhead 2 which contains suitable packing elements I to prevent the flow offluid around the piston head. A piston rod 3 extends downwardly througha drive bushing 5 and contains at the lower end thereof a tool joint box6 which contains attached thereto a suitable bit 9. Cylinder l containsports 4 at the lower part permitting passage of fluid from the areabetween the well bore hole and the cylinder, and the area between thepiston rod and the inner surface of the cylinder. The pressure below thepiston is thus relieved, resulting in a net downward force on thepiston. Nozzles I l are shown in the bit. A crosssection of theapparatus through section IIII is illustrated by Figure 2.

While the drawing has been described utilizing a drag or fishtail bit,it is to be understood that the present invention may be also utilizedwhen employing other bits, as for example, rock bits and the varioustypes of jet bits.

In operation the pressure of the mud or other drilling fluid on thepiston exerts a force on the bit through the piston rod or lower Kellyjoint. This joint, as shown in the cross section, Figure 2, is fluted orsquare in order that sufiicient torque may be applied to turn the bit.This permits the entire string of drill pipe to hang in tension. Thecontrol of the weight on the bit is secured first by the size of thenozzles in the bit and second by changes in the mud velocity.

This invention is particularly valuable when used with the so-called,jet bits which have recently been developed. These jets are designedwith small nozzles through which an extremely high velocity mud streamis passed. Bits of this kind have been found to drill much faster andmore economically than the conventional bits. In order to obtain theoptimum mud velocities when using this type of bit, a pressuredifferential through the nozzle of several hundred pounds is commonlyemployed. Bits of this kind generally employ nozzles of from to 1" indiameter. In this invention, the nozzle diameter would be used as amajor factor which would determine the weight to be carried on the bit.By way of example, suppose that the inside diameter of the cylinder were6" and that it were desired to hold a force on the bit of 20,000 lbs,the cross-sectional area of the cylinder would be approximately 28square inches and the pressure differential across the cylinder would beapproximately 700 lbs. Assume that two nozzles are Force OnBit(Thousands of Lbs.)

Nozzle Diameter (each) (For 2 Nozzles) A 1% is g G. P. M. MudCirculated:

The 6.'.-inside diameter cylinder would probably beused'whendrillingholesof a diameter ofapproximately 9 inches. For drillinglargerdiameter holes, it would bepossible to use a cylinder of largerdiameterand likewise smaller holes would demand that a smaller cylinder be used.The force on the bit,'of course, for a given rate of circulation andnozzle size will be directly proportionate to the cross-sectional areaof the cylinder.

The-invention. is. broadly concerned with the utilization of theheadfofthe drilling fluid Within thedrillv steinto secure the required force onthe bitduring a drilling operation. The invention may be used'when.employing any type of bit but is particularlylefiective with jet bits,which bitsareedesigned with relatively small nozzles in order to secureahigh velocity mud streamthroughthe bits Fromtheabove it is apparentthat the specific drilling conditions employed .whenutilizingthe presentinvention will be a function of various related conditions, as forexample, nozzle size; density. of the mud; the-rate otrnud circulation;and the diameter of the drilling-stemused. These factors vary appreciablydependingupon the formation being penetrated;' the diameter ofwell bore hole desi.red,-as well as,.upon otherdrilling conditions. Withother factorsmaintained constant, simple calculations'of the force.exerted on the bit assembly may be made bynoting that the pressure onthe piston is roughly proportioned to the square of .the velocity ofvthemud through the nozzles and inversely proportioned to the specificweight of the. mud. The nozzles diameters are generally in the rangefrom about to l. The diameters, however, will vary depending upon thenozzles in the bit .whichusually vary from 2 to 4 The diameter of thedrill string may vary from 2 to 7" and. higher, although usually thediameter is in the range from 4 to The density. ofv themud generally isin the range from 9. to 16--lbs..per gallon, although the density may,under certain conditions, be without this range. The quantity of mudcirculated is usually in the range from 200 to 1000 gallons per minute.The desired force in the bit, likewise, may vary appreciably as forexample in the range from 4,000 to 40,000 lbs. and higher.

A preferred method of operating infaccordance with the present'inventiom is that the driller lowers the drill pipe until such time asa slight reduction in the reading of the weight indicator atthesurface-indicates that the weight of the drills'tring is resting inpart on the lower Kelly joint. The driller then raises the drill stringa small distance "which assures the driller that the weight of thedrillpipe is not resting on the bit. The drillerthen continues to drill innormal fashion tor-such length of time as the driller might expect isrequired to make an amount of hole somewhat less than the maximum strokeof the lower Kelly joint. This will vary from a few minutes to anhour'ortwo depending on the hardness of the formation being drilled andthe progress being made. The driller then repeats the operation and inthis way it is possible to makesure the-tithe drill pipe is alwayshanging in tension throughout its length and that the bit is'on.the'bottom with the weight required.

Having described the invention, it is claimed:

Improved'drill bit assembly adapted to be attached to the: lower endofadrill string comprising a cylindrical. element, the upper end of whichis adapted to be attached to the lower end of saididrill string; a:drive bushing located within and attached to the lower end of saidcylindrical element, apiston head element within and movable withrespectto-said cylindrical element above the said drive bushing, a piston rodelementattached to said piston head element, said piston rod elementextending below the lower end of said cylindrical element and throughsaid drive bushing, aplurality'ci ports passing through said cylindricalelement immediately above the drive bushing, a drill bit characterizedby'containing a plurality of restricted nozzle passageways attached tothe lower end: of said piston rod element, said piston rod element beingcharacterized by being hollowandpreviding a conduit from'the area abovesaid piston head to said nozzle'passageways.

References Cited-in thefile or" this patent UNITED STATES PATENTS NumberName Date 1,357,554 Hughes Nov. 2, 1926 1,660,033 Braswell Feb. 21, 19281,686,945 Abercrombie Oct. 9, 1928 1,767,350 Crowell June 24, 19301,844,257 Lincoln Feb. 9, 1932 1,900,932 HolleStalle Mar. 14,19331,905,497 Peters Apr. 25, 1933 2,300,805 Pew Nov. 3,1942

